Ouch. I've been dragged down before, and it's no fun. Walking a mile plus home with a busted lip, skinned hands and knees and a wet butt from landing in a puddle, swearing that you will turn all three dogs into rugs.....
It sounds like you are walking him with the leash attached to his regular flat collar? I would recommend that you use a harness with a front attachment instead (the Balance harness from Blue9 is a good one), so that his pulling is redirected to the side, which gives you some leverage. You can also use a double ended leash, with one end clipped to the harness and the other to a martingale collar, so that you can still practice loose leash walking, but have the leverage on the front clip harness when you need it.
Also, this online class might help you learn leash handling and management skills for his excitement. Fenzi Dog Sports Academy - BH150: Management for Reactive Dogs
There is another class, a self study one, not live like the other I mentioned, on a method of teaching loose leash walking and reducing the over-excitement about birds and such, but I'm not sure how easy it would be on a crowded city sidewalk. Fenzi Dog Sports Academy - EW100: Reducing Overarousal and Reactivity via the Circle Method of Leash Walking
It sounds like you are walking him with the leash attached to his regular flat collar? I would recommend that you use a harness with a front attachment instead (the Balance harness from Blue9 is a good one), so that his pulling is redirected to the side, which gives you some leverage. You can also use a double ended leash, with one end clipped to the harness and the other to a martingale collar, so that you can still practice loose leash walking, but have the leverage on the front clip harness when you need it.
Also, this online class might help you learn leash handling and management skills for his excitement. Fenzi Dog Sports Academy - BH150: Management for Reactive Dogs
There is another class, a self study one, not live like the other I mentioned, on a method of teaching loose leash walking and reducing the over-excitement about birds and such, but I'm not sure how easy it would be on a crowded city sidewalk. Fenzi Dog Sports Academy - EW100: Reducing Overarousal and Reactivity via the Circle Method of Leash Walking